Minimal decoding method for spatially multiplexing digital video pictures

ABSTRACT

Multiple video picture frames are combined into a spatial multiplex video picture frame that may be fully decoded and displayed. The video display of the spatial multiplex video picture frame is a composite combination of all of the video picture frames that have been combined, and may have an appearance such as a mosaic. Multiplexing the video picture frames involves removing picture headers, creating a picture header for the spatial multiplex video picture frame, and altering the headers of individual components of each video picture frame. The new header for the spatial multiplex video picture frame indicates a slice format frame, and headers of the individual components are altered to provide a slice format based picture position for each video picture frame. The headers of the individual components are altered to become slice based, such as in accordance with the ITU-T H.263 video standard, prior to establishing the slice based picture position if the frames are not already of the slice format.

TECHNICAL FIELD

The present invention relates to combining multiple digital videopicture frames into a single spatial multiplex video picture frame toproduce a single displayed picture that is a composite of severalindividual pictures. More particularly, the present invention relates togenerating the spatial multiplex video picture frame by altering headerinformation of the individual video picture frames being combined.

BACKGROUND

A motion picture such as broadcast television is made of individualpictures that are rapidly displayed to give the illusion of continuousmotion. Each individual picture in the sequence is a picture frame. Adigitally encoded picture frame is made of many discrete pictureelements, or pixels, that are arranged in a two-dimensional array. Eachpixel represents the color (chrominance) and brightness (luminance) atits particular point in the picture. The pixels may be grouped forpurposes of subsequent digital processing (such as digital compression).For example, the picture frame may be segmented into a rectangular arrayof contiguous macroblocks, as defined by the ITU-T H series codingstructure. Each macroblock typically represents a 16×16 square ofpixels.

Macroblocks may in turn be grouped into picture frame components such asslices or groups of blocks, as defined under the ITU-T H.263 videocoding structure. Under H.263, a group of blocks is rectangular andalways has the horizontal width of the picture, but the number of rowsof group of blocks per frame depends on the number of lines in thepicture. For example, one row of a group of blocks is used for pictureshaving 4 to 400 lines, two rows are used for pictures having 404 to 800lines, and four rows are used for pictures having 804 to 1152 lines. Aslice, on the other hand, is a flexible grouping of macroblocks that isnot necessarily rectangular. Headers within the encoded video picturebit stream identify and provide important information about the varioussubcomponents that make up the encoded video picture. The picture frameitself has a header, which contains information about how the pictureframe was processed. Each group of blocks or slice within a videopicture frame has a header that defines the picture frame component asbeing a slice or group of blocks as well as providing informationregarding the placement of the component within the picture frame. Eachheader is interpreted by a decoder when decoding the data making up thepicture frame in preparation for displaying it.

In certain applications, displaying multiple picture frames within asingle display is desirable. For example, in videoconferencingsituations it is useful for each participant to have a video displayshowing each of the other participants at remote locations. Visual cuesare generally an important part of a discussion among a group ofparticipants, and it is beneficial for each participant's display topresent the visual cues of all participants simultaneously. Any methodof simultaneously displaying all the conference participants is called acontinuous presence display. This can be accomplished by using multipledecoders and multiple video displays at each site, or by combining theindividual video pictures into a single video picture in a mosaicarrangement of the several individual pictures (called a spatialmultiplex).

Multiplexing picture frames into a single composite picture framerequires some form of processing of each picture frame's encoded data.Conventionally, a spatial multiplex video picture frame could be createdby completely decoding each picture frame to be multiplexed to abaseband level, multiplexing at the baseband level, and then re-encodingfor transmission to the various locations for display. However, decodingand re-encoding a complete picture frame is computationally intensiveand generally consumes a significant amount of time.

The H.263 standard provides a continuous presence multipoint and videomultiplex mode that allows up to four individual picture frames to beincluded in a single bitstream, but each picture frame must beindividually decoded by individual decoders or by one very fast decoder.No means of simultaneously displaying the pictures is specified in thestandard. Additionally, time-consuming processing must be applied to thepicture frames after they have been individually decoded to multiplexthem together into a composite image for display.

Therefore, there is a need in the art for a method and system that canspatially multiplex multiple picture frames into a single picture framewithout requiring each individual picture frame to be fully decoded whenbeing multiplexed and without requiring additional processing afterdecoding to multiplex the picture frames.

SUMMARY

The present invention spatially multiplexes several picture frames intoa single spatial multiplex video picture frame by manipulating headerinformation for the picture frame components, such as the groups ofblocks or slices, containing the picture frame data. A picture headerassociated with each picture frame is removed and a new picture headeris generated that applies to the spatial multiplex video picture framethat is a composite of all of the individual picture frames. The newheader provides an indication of a slice format for the spatialmultiplex video picture frame. The component headers of each pictureframe are altered to set a slice format based picture position for thepicture frame within the picture that results from the spatial multiplexvideo picture frame. The slice format is prevalent within the H.263standard. Thus, only the component headers need to be decoded andre-encoded to establish the spatial multiplex video picture frame.

The spatial multiplex video picture frame results from concatenating thenew picture header together with the picture frames having the alteredcomponent header information. The spatial multiplex video picture framemay then be decoded as if it were a single picture frame to display thecomposite of the several individual picture frames Displaying thespatial multiplex video picture frame allows the individual pictureframes to be viewed simultaneously on one display screen.

The system that multiplexes the individual picture frames may be ascalable facility such that as the need for picture frame multiplexingincreases, the system may be expanded to fill the need. The systemincludes a plurality of computing devices, such as single boardcomputers, linked to a data packet switch through a serial interface.Each computing device within the system has the ability to combineindividual picture frames into a single spatial multiplex video pictureframe by altering the headers of the picture frame components to set aslice format based picture position for the picture frames. As the needfor additional processing arises, additional computing devices incommunication with the data packet switch may be added to provideadditional capacity.

The present invention may be employed in a networked environment where aprocessing device, such as a network server, communicates with severalclient devices, such as videoconferencing devices. The processing devicereceives the multiple picture frames from various communication channelsin the network. For example, the processing device may receive a streamof video picture frames from each participant in a videoconferencethrough the network. The processing device then multiplexes theindividual picture frames into a spatial multiplex video picture frameby altering the component header information to produce a slice basedpicture position for each frame. The spatial multiplex video pictureframe is transmitted back through the communication channels of thenetwork where it can be displayed by the display screen of the clientdevices.

The present invention may also be employed in a networked environmentwhere each video site, such as a videoconferencing device, generatesvideo picture frames. The picture frames are transmitted to other videosites in the network, and picture frames produced by other video sitesare received. The video site multiplexes the picture frames to producesthe multiplexed composite picture frame by altering the component headerinformation to set a slice format based picture position. The video sitemay then decode the spatial multiplex video picture frame and displayit.

The various aspects of the present invention may be more clearlyunderstood and appreciated from a review of the following detaileddescription of the disclosed embodiments and by reference to thedrawings and claims.

DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a composite picture frame and slice structure, anindividual picture frame that may be multiplexed into the compositepicture frame, and alternative picture frame structures.

FIG. 2 is an exemplary picture layer syntax of a picture frame under theH.263 standard.

FIG. 3 is an exemplary group of blocks layer syntax under the H.263standard.

FIG. 4 is an exemplary slice layer syntax under the H.263 standard.

FIG. 5 is an operational flow for multiplexing picture frames utilizedby one embodiment of the present invention.

FIG. 6 is an operational flow of the group of blocks to slice formatconversion utilized by the embodiment.

FIG. 7. is a block diagram of an embodiment employing single-pointprocessing in a network environment.

FIG. 8 is a block diagram of an embodiment employing on-site processingin a networked environment.

FIG. 9 is a block diagram of an embodiment of a scalable multiplexingfacility.

DETAILED DESCRIPTION

FIG. 1 illustrates a display of a spatial multiplex video picture frame100 made up of individual picture frames 102. As shown, the spatialmultiplex video picture frame 100 includes sixteen picture frames 102 ofindividual people participating in a videoconference where the pictureframes 102 form a mosaic pattern. Because each participant is always inview, the spatial multiplex video picture frame 100 is referred to as acontinuous presence display. As will be discussed below, each individualpicture frame 102 of the spatial multiplex video picture frame 100 isinitially a normal picture frame 104 that may be displayed in full sizeon a display screen. The picture frame 104 may be represented as datathat is encoded and segmented in various ways.

For the example shown, the picture frame 104 may have been transmittedin a quarter-size common image format (QCIF) indicating a pixelresolution of 176×144. In such a case, the spatial multiplex videopicture frame 100 is decoded as a 4CIF picture indicating a resolutionof 704×576 because it contains sixteen QCIFs where four QCIFs form a CIFsize image. It is to be understood that other picture size formats forthe individual picture frames 104 and for the spatial multiplex videopicture frame 100 are possible as well. For example, the multiplexedimage may contain 64 individual QCIF picture frames and therefore have a16CIF size.

The group of blocks format 110 is one alternative for segmenting andencoding the picture frame 104. The picture frame 104 of the group ofblocks format 110 includes one or more rows of picture components knownas groups of blocks 124. In the example, shown, the QCIF frame 104 hasthree rows of groups of blocks. A picture header 122 is also included.The picture header provides information to a decoder when the pictureframe 104 is to be displayed in full size and tells the decoder that thepicture frame 104 has a group of blocks format 110.

Each row 124 is made up of an array 112 of macroblocks 128 that definethe luminance and chrominance of the picture frame 104. Each row 124also includes a header 126 that tells the decoder the position withinthe picture frame 104 where the row of group of blocks 124 belongs. Inthe example shown, the group of blocks 124 has two rows of macroblocks128 because it is intended for the picture frame 104 to be displayedwith 404 to 800 total lines. In reality, a group of blocks 124 will havemany more macroblocks 128 per row than those shown in FIG. 1.

As discussed above, the group of blocks format defined by the H.263standard requires that the row 124 always extends to the full width ofthe picture. Therefore, a direct remapping of a group of blocks format110 to a spatial multiplex video picture frame 100 is not possiblebecause the spatial multiplex video picture frame 100 requiresindividual frames to have a width that may be less than the full widthof the picture. In the videoconferencing context, several participantsmay need to be displayed across the width of the picture as shown inFIG. 1, and a group of blocks format 110 does not permit such remapping.

An alternative format for segmenting and encoding the picture frame 104is the slice format 106, such as defined by the H.263 standard. Theslice format 106 is more flexible and does not require each slice tomaintain the full width of the picture. The slice format 106 includesone or more picture components known as slices 116 that may or may notextend across the full width of the picture, and a picture header 114that specifies to the decoder that the picture frame 104 has a sliceformat. Each slice 116 is made up of a grouping 108 of macroblocks 120.Each slice 116 also has a slice header 118 that indicates to the decoderthe relative position of the slice in the picture 104.

The slice format 106 of the picture frame 104 allows the picture frame104 to be multiplexed into the composite picture frame 100 with minimaldecoding. The spatial multiplex video picture frame 100 may be createdin a slice format 130 of many slices 134 corresponding to the slices 116of the individual picture frames 102 forming the composite. As shown,the slices 134 have a width that is less than the picture width so thatmultiple slices 134 are provided for each row of slices of the picture.A new picture header 132 is also generated to indicate to the decoderthat the picture frame 100 is of the slice format 130 and is of a 4CIFsize, 16CIF size, and so on. The header, such as 118, of each slice 134is modified to properly position the slice within the spatial multiplexvideo picture frame 100.

FIG. 2 shows the picture layer syntax 200 that is made up of the pictureheader included at the beginning of each picture frame as well as thegroup of block layer or slice layer. The picture layer syntax 200includes a picture start code (PSC) 202 that signifies the beginning ofa new picture frame. A temporal reference (TR) 204 follows in thebitstream and provides a value indicating the timing of display of thepicture frame relative to a previous frame and the picture clockfrequency. A PTYPE block 206 follows and provides information about thepicture such as whether the source format of the picture frame is aquarter-size common image format (QCIF), a CIF format, or other.

The picture layer syntax 200 may also include a PLUS HEADER block 208that contains information about the picture frame, including whether theframe consists of groups of blocks or slices. A PQUANT block 210provides quantizer information to configure the quantization parametersused by the decoder. An optional continuous presence multipoint (CPM)block 212 signals the use of continuous presence multipoint and videomultiplex mode discussed above that permits multiple individual framesto be included in the bitstream. As discussed the CPM mode causes theindividual frames to maintain their identities as individual frames andrequires that they be individually decoded and then processed to form asingle image. A picture sub-bitstream indicator (PSBI) 214 may beincluded if CPM mode is indicated. CPM mode may be implemented inconjunction with the logical operations of FIGS. 5 and 6 to providesub-bitstreams that are themselves multiplexed bitstreams, or CPM may beturned off if only the logical operations of FIGS. 5 and 6 are desiredfor providing continuous presence video.

A temporal reference for B-picture parts (TRB) 216 may be included if aPB-frame is indicated by the PTYPE block 204 or PLUS HEADER block 208. ADBQUANT block 218 may also be included if a PB-frame is indicated toindicate the relation of the BQUANT quantization parameter used forB-picture parts in relation to the QUANT quantization parameter used forP-picture parts. A PEI block 220 includes a bit that signals thepresence of the supplemental enhancement information (PSUPP) block 222.PSUPP block 222 defines extended capabilities for picture decoding. Thegroup of blocks (GOB) layer 224 or slice layer 226 then follows in thebitstream. The GOB layer 224 contains each group of block of the pictureframe and is discussed in more detail in FIG. 3. Slice layer 226contains each slice of the picture frame and is discussed in more detailin FIG. 4.

The ESTUF block 228 is included to provide mandatory byte alignment inthe bitstream. The end of sequence (EOB) block 234 may be included tosignal the end of the sequence of group of blocks or slices.Alternatively, the end of sub-bitstream sequence (EOSBS) block 230 maybe included to indicate an end of a sub-bitstream when in CPM mode. Anending sub-bitstream indicator (ESBI) block 232 is included to providethe sub-bitstream number of the last sub-bitstream. The PSTUF block 236is included to provide byte alignment for the PSC of the next pictureframe.

FIG. 3 shows the group of blocks layer syntax 300 that is made up of thecomponent header and the macroblocks of the array forming a group ofblocks and that would be found in each group of blocks of the group ofblocks layer 224 of FIG. 2. A GSTUF block 302 is included to providebyte alignment for a group of blocks start code (GBSC) 304. The GBSC 304indicates to the decoder the start of a group of blocks. A group number(GN) block 306 indicates the group of block number that defines theposition of the group of blocks in the picture frame. A GOBsub-bitstream indicator (GSBI) 308 may be included when in CPM mode toindicate the sub-bitstream number.

A GOB frame ID (GFID) 310 is included to indicate the particular framethat the group of blocks corresponds to. GQUANT block 312 providesquantizer information to control the quantization parameters of thedecoder. A temporal reference indicator (TRI) block 314 is included toindicate the presence of a temporal reference when operating in areference picture mode. A temporal reference (TR) block 316 is includedto provide a value indicating the timing of display of the group ofblocks relative to a previous group of blocks and the picture clockfrequency. A temporal reference for prediction indication (TRPI) block318 is included to indicate the presence of a temporal reference forprediction field (TRP) 320. The TRP field 320 indicates the temporalreference to be used for prediction of the encoding.

A back channel message indication (BCI) field 322 is included toindicate whether a message is to be delivered from the decoder back tothe encoder regarding conditions of the received coded stream. A backchannel message (BCM) layer 324 contains a message that is returned froma decoder to an encoder in order to tell whether forward-channel datawas correctly decoded or not. A macroblock (MB) layer 326 contains amacroblock header and the macroblock data for the group of blocks.

FIG. 4 shows the slice layer syntax 400 that is made up of the componentheader and the macroblocks of the array forming a slice and that wouldbe found in each slice of the slice layer 226 of FIG. 2. An SSTUF block402 is included to provide byte alignment for a slice start code (SSC)block 404 indicating the beginning of a slice. A first slice emulationprevention bit (SEPB1) 406 is included to prevent start code emulationafter the SSC block 404. A slice sub-bitstream indicator (SSBI) block408 is included when in CPM mode to indicate the sub-bitstream number ofthe slice. A macroblock address (MBA) field 410 is included to indicatethe first macroblock of the slice as counted from the beginning of thepicture in scanning order to set the position of each slice in thepicture frame.

A second slice emulation prevention bit (SEPB2) block 412 is alsoincluded to prevent start code emulation after the MBA field 410. AnSQUANT block 414 is included to provide quantizer information thatcontrols the quantization parameters of the decoder. A slice widthindication (SWI) block 416 is provided to indicate the width of thecurrent rectangular slice whose first macroblock is specified by the MBAfield 410. A third slice emulation prevention bit (SEPB3) 418 isincluded to prevent start code emulation after the SWI block 416. Aslice frame ID (GFID) 420 is included to indicate the particular pictureframe that the slice corresponds to. The TRI field 422, TR field 424,TRPI field 426, TRP field 428, BCI field 430, BCM layer 432, and MBlayer 434 are identical to the fields of FIG. 3 that go by the samename.

The operational flow of the process 500 for multiplexing individualpicture frames containing the GOB syntax 300 or the slice syntax 400into a single picture frame is shown in FIG. 5. In this embodiment ofthe operational flow, it is assumed that the single picture frames areoriginating from encoder devices and are being processed by one or moredecoder devices after transfer, such as through a network medium asshown in the systems of FIGS. 7 and 8. The process 500 begins at calloperation 502 where the two devices passing the picture data establish acommon mode of operation suitable for generating continuous presencevideo. The common mode of operation includes a consistent usage ofheader information so that, for example, back channel messaging isemployed between the encoder and decoder or other enhanced capabilitiesare realized. After communication is established, start operation 504causes one device of the connection to broadcast a start indicator thatallows synchronization of transmission of the individual picture framesfrom the various sources, such as the remote locations of thevideoconference.

Once the picture frames to be included in the multiplexed frame havebeen received, header operation 506 reads the picture layer header, suchas shown in FIG. 2, for each individual picture frame and discards them.This requires that only the picture header be decoded. A single newpicture layer header that applies to the spatial multiplex video pictureframe is created and encoded at header operation 506. The single newpicture layer header provides in the PTYPE field 206 an indication thatthe spatial multiplex video picture frame is of a size capable ofincluding the number of individual frames being multiplexed. The PLUSHEADER field 208 of the new picture header is configured to indicate arectangular slice format.

After substituting the new picture header, the component header of oneof the individual frames is interpreted at read operation 508 inpreparation for subsequent processing discussed below includingconversion to a slice format and repositioning within the multiplexedimage. Query operation 510 detects whether the picture header read inheader operation 506 for the current picture frame indicates a group ofblocks format. If a group of blocks format is detected, then conversionoperation 512 converts the group of blocks headers into slice headers.Conversion operation 512 is discussed in greater detail below withreference to FIG. 6. If a group of blocks format is not detected, thenthe conversion operation 512 is skipped since a slice format is alreadypresent in the picture frame.

After finding or converting to a slice format, macroblock operation 514alters the MBA 410 within each slice of each picture frame to positionthe slice within a particular region of the spatial multiplex videopicture frame. For example, one individual picture frame must go in thetop left-hand corner of the multiplexed picture so the top-leftmostslice of that picture frame is given an MBA 410 corresponding to the topleft-hand corner position. The component header is also re-encoded atthis operation after the MBA 410 has been altered. The slice is theninserted into the proper location in the continuous presence picturestream by concatenating the bits of the slice with the bits alreadypresent in the picture stream including the new picture header at streamoperation 516. The picture stream may be delivered as it is beinggenerated at transmit operation 518 wherein the current slice is writtento an output buffer and then transmitted to a network interface.

After writing the slice to the output buffer, query operation 520detects whether the last slice was the end of the continuous presence orspatial multiplex video picture frame. If it was not the last slice ofthe multiplexed frame, then flow returns to read operation 508 where theheader of the next group of blocks or slice to be included in thespatial multiplex video picture frame is read. If query operation 520determines that the last slice was the end of the spatial multiplexvideo picture frame, then flow returns to header operation 506 whereinthe picture headers for the next set of individual picture frames areread and discarded.

FIG. 6 shows the operational flow of the conversion operation 512.Conversion operation 512 begins at alignment operation 602 where theGSTUF field of the GOB syntax 300 is converted to an SSTUF field of theslice syntax 400 by adjusting the length of the stuff code to providebyte alignment of the next code element. At start code operation 604,the GBSC 304 is maintained because it is already identical to the SSC404 needed in the slice syntax 400. At prevention operation 606, theSEPB1 406 is inserted into the bitstream to later prevent start codeemulation when being decoded.

Translation operation 608 converts the GSBI 308 to the SSBI 408. Duringthis operation, GSBI ‘00’°becomes SSBI ‘1001’, GSBI ‘01’ becomes SSBI‘1010’, GSBI ‘10’ becomes SSBI ‘1011’, and GSBI ‘11’ becomes SSBI‘1101’. At MBA operation 610, the GN 306 is replaced by an MBA 410chosen to place the slice in its designated location within thecomposite picture frame resulting from multiplexing the individualpicture frame bitstreams. Prevention operation 612 then places a SEPB2into the bitstream to prevent start code emulation. At quantizeroperation 614, GQUANT is maintained in the bitstream after SEPB2 becauseGQUANT is already identical to SQUANT 414.

Slice operation 616 then sets the width of the slice, or SWI 416, to thewidth of the GOB in terms of the number of macroblocks. This is possiblebecause the slice structure selection (SSS) field (not shown) of thePLUS HEADER field 208 of the picture syntax 200 of FIG. 2 has been setto the rectangular slice mode in header operation 506 of FIG. 5.Prevention operation 618 then inserts a SEPB3 into the bitstream toprevent start code emulation when the slice is decoded. At GFIDoperation 620, the GFID 310 is maintained in the bitstream after SEPB3because it is already identical to GFID 420. In substitute operation622, all remaining portions of the GOB syntax 300 are maintained in thebitstream because they are also identical to the remaining portions ofthe slice syntax 400.

FIG. 7. shows one network environment for hosting a continuous presencevideoconference. A server 702 communicates through bi-directionalcommunication channels 716 with client devices 704, 706, 708, and 710.Each client device, such as a personal computer or special-purposevideoconferencing module, is linked to a camera 712 or other videosource and a video display 714. The client devices transmit sequences ofencoded picture frames produced by the camera 712 or other video sourceto the server 702 though the communication channels 716. The server 702then employs the processes of FIGS. 5 and 6 to combine all of theencoded picture frames into an encoded spatial multiplex video pictureframe. The server 702 then transmits the spatial multiplex video pictureframe back through the communications channels 716 to the client deviceswhere it is decoded and displayed on each display screen 714. Thus, theclient devices may include encoder and decoder processing but do notneed to include the multiplexing processing discussed above.

Four client devices are shown only for exemplary purposes, and it is tobe understood that any number of client devices may be used subject tothe limitation on the total number of individual frames to be includedon the display 714. It is also to be understood that each individualframe to be included in the multiplexed frame through the processes ofFIGS. 5 and 6 does not have to be of the same size, such that one framemay occupy more screen area than others. For example, the frame showingthe person currently speaking in a videoconference may be enlargedrelative to frames showing other participants. One skilled in the artwill recognize that negotiation between participating devices can beestablished such that mode switching can occur to permit one or moreparticipants to provide one image size (e.g., QCIF) while otherparticipants provide a different image size (e.g., CIF), subject to theability to combine the image sizes into a composite that will fit on theintended display. Furthermore, it is to be understood that the server702 may customize each videostream being returned to each client device704, 706, 708, and 710, such as by removing the frame provided by therecipient client device from the spatial multiplex being returned orcreating the spatial multiplex from some other subset.

The communication channel between the client devices 704, 706, 708, and710 and the server 702 can be of various forms known in the art such asconventional dial-up connections, asymmetric digital subscriber lines(ADSL), cable modem lines, Ethernet, and/or any combination. An InternetService Provider (ISP) (not shown) may be provided between the server702 and each client device, or the server 702 may itself act as an ISP.The transmissions through a given channel 716 are asymmetric due to onepicture frame being transmitted to the server 702 from each clientdevice while the server 702 transmits a concatenation of picture framesforming the multiplexed bitstream back to each client device. Therefore,ADSL is well suited to picture frame transfer in this networkconfiguration since ADSL typically provides a much greater bandwidthfrom the network to the client device.

FIG. 8 shows an alternative network configuration where each clientdevice 802, 804, 806, and 808 has its own processing device performingthe operations of FIGS. 5 and 6. Each client device is linked to acamera 810 or other video source and a display 812. A bi-directionalcommunication path 814 interconnects each client device to the others.The bi-directional communication paths 814 can also be of various formsknown in the art such as conventional dial-up connections, asymmetricdigital subscriber lines (ADSL), cable modem lines, Ethernet, and/or anycombination. One or more ISPs (not shown) may facilitate transferbetween a pair of client devices.

Each client device generates an encoded picture frame sequence that istransmitted to the other client devices. Thus, each client devicereceives an encoded picture frame from the other client devices. Theclient device may then perform the multiplexing operations discussedabove to create the spatial multiplex video picture frame that isdisplayed.

Multiplexing the individual picture frames together at each clientdevice where the spatial multiplex video picture frame will be displayedallows each client device to have control over the spatial multiplexvideo picture frame it will display. For example, the client device canchoose to exclude certain picture frames or alter the displayed size ofparticular picture frames. In a videoconference, the client device maychoose to eliminate the picture frame that it generates and sends toothers from the spatial multiplex video picture frame that it generatesand displays. Because each client device performs the multiplexingoperations, the communication paths 814 carry only the individualpicture frame sequences generated by each sending client device ratherthan spatial multiplex video picture frame sequences.

FIG. 9 shows an example of a scalable multi-point conferencing facility900. The facility includes a packet switch 902, such as a multi-gigabitEthernet switch, linked to several processing modules, such as singleboard computers (SBCs) 904, 906, and 908. An SBC generally refers to acomputer having a single circuit board including memory, magneticstorage, and a processor for executing a logical process such as thoseof FIGS. 5 and 6. The processing modules may include general-purposeprogrammable processors or dedicated logic circuits depending upon theperformance necessary. Because the operations of FIGS. 5 and 6 to beperformed by the processing modules requires only decoding of headerinformation, programmable processors are adequate for continuouspresence processing in real time for most implementations.

The processing modules are linked to the packet switch 902 throughhigh-speed serial interfaces 910, such as Fast/Gigabit Ethernet. Thepacket switch 902 receives encoded picture frame sequences from clientdevices, such as discussed with reference to FIG. 7, but possibly fromseveral videoconferencing sessions. The packet switch 902 may then sendall picture frame sequences corresponding to a particularvideoconference to one of the processing modules 904, 906, or 908. Theprocessing module multiplexes the picture frames to generate a spatialmultiplex video picture frame and sends the spatial multiplex videopicture frame sequence back to the packet switch 902. The packet switch902 then delivers the spatial multiplex video picture frame sequenceback to client devices of the particular videoconference.

Thus, the scalable multi-point conferencing facility 900 can providemultiplexing services for multiple videoconference groupssimultaneously. As the number of videoconference groups at any giventime increases or decreases, the processing modules employed by thepacket switch 902 can be added or removed from active service and madeavailable for other duties when not needed by packet switch 902.

Although the present invention has been described in connection withvarious exemplary embodiments, those of ordinary skill in the art willunderstand that many modifications can be made thereto within the scopeof the claims that follow. Accordingly, it is not intended that thescope of the invention in any way be limited by the above description,but instead be determined entirely by reference to the claims thatfollow.

1-20. (canceled)
 21. An apparatus for creating a combined video imageincluding multiple video images from a plurality of video images, whereeach video image has an image header and a plurality of video imagecomponents and each video image component has an image component header,the apparatus comprising: a serial interface to a data packet switch;and a processor configured to: remove the image header from each videoimage to be included in the combined video image, wherein each videoimage is received via the data packet switch; generate a new imageheader for the combined video image, the new image header indicating acombined format; alter the image component headers of each video imageto be included in the combined video image to set a combined formatbased image position for the video image within an image produced by thecombined video image; and generate the combined video image byconcatenating the new image header together with the plurality of videoimages having no image header and having the altered image componentheaders.
 22. The apparatus of claim 21, wherein the apparatus isconfigured to transmit the combined video image to the data packetswitch.
 23. The apparatus of claim 21, wherein the processor includes asingle microprocessor.
 24. The apparatus of claim 21, wherein the datapacket switch is an Ethernet switch, and the serial interface is anEthernet interface.
 25. The apparatus of claim 21, wherein the pluralityof video images are from a set of QCIF, CIF, and 4CIF video images. 26.An apparatus for creating a continuous presence display of a combinedvideo image including multiple video images from a plurality of videoimages, where each video image has an image header and a plurality ofvideo image components and each video image component has an imagecomponent header, the apparatus comprising: an interface to a networkhaving a plurality of communication channels; and a processor incommunication with the plurality of communication channels via theinterface, wherein the processor is configured to: receive the multiplevideo images from multiple video sources through the communicationchannels; remove the image headers from the multiple video images;generate a new image header for the combined video image with the newimage header indicating a combined format; decode and alter the imagecomponent headers of the video images to set a combined format basedimage position within an image produced by the combined video image;re-encode the image component headers, and generate the combined videimage by concatenating the new image header together with the pluralityof video images having no image header and having the altered imagecomponent headers, wherein the combined video image is transmitted tothe plurality of communication channels.
 27. The apparatus of claim 26,wherein the apparatus is included in at least one of a plurality ofvideo sites that are in communication with the plurality ofcommunication channels, and the processor is further configured toencode and transmit the combined video image to other video sites andreceive and decode the combined video image received from the othervideo sites via the plurality of communication channels, and theapparatus further comprises a display for presenting for display thedecoded combined format video image.
 28. The apparatus of claim 26,wherein the apparatus is in communication with the plurality ofcommunication channels through an asymmetrical digital subscriber line.29. The apparatus of claim 26, wherein the combined format based imageposition for each video image is a unique image position, and thecombined video image represents a mosaic of the video images.
 30. Anapparatus for creating a combined video image including multiple videoimages from a plurality of video images, where each video image has animage header and a plurality of video image components and each videoimage component has an image component header, the apparatus comprising:a serial interface to a data packet switch; and a processor including asingle microprocessor configured to: remove the image header from eachvideo image to be included in the combined video image, wherein eachvideo image is received via the data packet switch; generate a new imageheader for the combined video image, the new image header indicating acombined format; alter the image component headers of each video imageto be included in the combined video image to set a combined formatbased image position for the video image within an image produced by thecombined video image; generate the combined video image by concatenatingthe new image header together with the plurality of video images havingno image header and having the altered image component headers; andtransmit the combined video image to the data packet switch.